*Excludes Observations that spanned multiple years
| Pre 1970 | 6 |
|---|---|
| 1970 | 0 |
| 1971 | 1 |
| 1972 | 1 |
| 1973 | 0 |
| 1974 | 0 |
| 1975 | 1 |
| 1976 | 0 |
| 1977 | 1 |
| 1978 | 0 |
| 1979 | 3 |
| 1980 | 5 |
| 1981 | 4 |
| 1982 | 3 |
| 1983 | 1 |
| 1984 | 1 |
| 1985 | 6 |
| 1986 | 0 |
| 1987 | 1 |
| 1988 | 78 |
| 1989 | 141 |
| 1990 | 131 |
| 1991 | 119 |
| 1992 | 199 |
| 1993 | 226 |
| 1994 | 318 |
| 1995 | 254 |
| 1996 | 369 |
| 1997 | 344 |
| 1998 | 380 |
| 1999 | 325 |
| 2000 | 160 |
| 2001 | 35 |
| 2002 | 28 |
| 2003 | 31 |
| 2004 | 15 |
| 2005 | 7 |
| 2006 | 15 |
| 2007 | 20 |
| 2008 | 20 |
| 2009 | 39 |
| 2010 | 72 |
| 2011 | 43 |
| 2012 | 79 |
| 2013 | 73 |
| 2014 | 37 |
| 2015 | 49 |
| 2016 | 68 |
| 2017 | 30 |
| 2018 | 24 |
| 2019 | 19 |
| 2020 | 13 |
| 2021 | 38 |
| 2022 | 48 |
| 2023 | 13 |
| 2024 | 20 |
| Total | 3914 |